For manufacturing a protective insulation film of a flexible printed circuit board, polyimide resin, polyurethane resin, polyamideimide resin or epoxy resin is generally employed. These resins are utilized in the form of a curable resin composition, if necessary, after addition of a curable compound.
The protective insulation film preferably has high flexibility, high bendability and low warping property in addition to high heat resistance, high resistance to chemical materials, and high resistance to solvents.
U.S. Pat. No. 6,335,417 B1 describes a modified polyimide resin which can give an article having high heat resistance, good pliability, and low warping property. The modified polyimide resin comprises recurring units composed of polyimide units containing polybutadiene moiety and units of residue derived from a diisocyanate.
JP-A-11-12500 describes a curable modified polyamideimide resin having a carbonate bonding.
JP-A-2002-145981 describes a curable modified polyimide resin having a carbonate bonding. The modified polyimide resin described in this publication is prepared by reacting a diisocyanate compound having a carbonate bonding in its main skeleton and a tetracarboxylic acid dianhydride.
The present inventors have noted that the curable modified polyamideimide resin having an amide bonding (which is described in JP-A-11-12500) shows a relatively high hygroscopicity. The high hygroscopicity causes decrease of insulation property of an insulation film of the modified polyamideimide resin formed on an electronic device.
According to the study of the present inventors, the modified polyimide resin having a carbonate bonding described in JP-A-2002-145981 shows a limited solubility in organic solvents. Further, an insulation film produced of the modified polyimide resin does not show satisfactory resistance under high temperature-high humidity conditions.